It is known that, in order to obtain the optimum reinforcing properties imparted by a filler in a tire tread, and thus to obtain high wear resistance, it is generally advisable for this filler to be present in the elastomeric matrix in a final form that is both as finely divided as possible and as uniformly distributed as possible. However, such conditions can be achieved only if this filler has a very good capacity, on the one hand, to be incorporated into the matrix during the mixing with the elastomer and to deagglomerate, disperse and become uniformly distributed in this matrix.
In order to improve the dispersibility of the filler in the elastomeric matrix, it is known practice to make use of a mixture of elastomer and filler in the “liquid” phase. To do this, use is made of an elastomer in latex form and an aqueous dispersion of the filler, commonly referred to as “slurry”.
In this field, as early as 1955, the problem of the uniform dispersion of fillers, and especially of carbon black, in rubber had already been raised. Thus, a process for preparing a masterbatch of rubber and of carbon black in the liquid phase is known from document BE 541816. This process is carried out continuously and uses hydraulic shocks or violent mechanical stirring to disperse the carbon black in the elastomeric matrix. Moreover, although this process works with carbon-based fillers, such as carbon blacks, which spontaneously coagulate with natural rubber, it does not make it possible to obtain coagulation with synthetic elastomers. It is therefore necessary to add a “coagulating” agent enabling the agglomeration, and hence coagulation, with synthetic elastomers.
Coagulating agent in the aqueous phase is intended to mean salts such as sodium chloride, acids such as hydrogen chloride, or else bases such as sodium hydroxide.
More recently, document WO 97/36724 discloses a process for preparing a masterbatch and specific equipment making it possible to improve the dispersibility of carbon black in a natural rubber latex. This technology meets two objectives: carrying out the coagulation step in the absence of coagulating agent, and obtaining a masterbatch in which the distribution of the filler is uniform. However, this technology has a certain number of drawbacks. The equipment used is very complex and the process described relies on very precise characteristics linked to this equipment, such as a defined coagulation zone geometry or else a defined flow speed difference.